I recently changed my paid app model to in-app purchase model, its easy to detect that the users who already purchased the app will not get the in-app purchase options when they update the app.
But the problem if these users delete the app and download again or they download in new device, then how to detect that the app is previously purchased.
I am not talking about in-app purchase or restore purchase. I want to detect user who purchased app from app store not from in-app purchase.